This invention relates to an improved single use hypodermic safety syringe, and more specifically to a plunger within the syringe which permits a conventional inoculation needle to be retracted to a position within the plunger.
Hypodermic syringes are well known in the art having been used for many years in the medical profession. In recent years the problem of a person using a syringe and becoming infected by an inadvertent prick from a used inoculation needle has intensified the search for a hypodermic syringe which protects those who might have to handle it.
Several devices have used a spring-loaded cover to shield an inoculation needle after it has been withdrawn from a person receiving an inoculation. For instance see U.S. Pat. No. 4,900,311 to Stern et at., U.S. Pat. No. 4,955,868 to Klein, or U.S. Pat. No. 4,966,592 to Burns et al. In each of these devices, the shield becomes rather unwieldy because it has to have a rather large cross-section so as so slide around the syringe barrel. The large cross-section prevents the person using the hypodermic syringe from accurately locating an insertion point because the insertion point is covered by the shield. Also since the inoculation needle is capped after the needle is used, an elongated shape is maintained. The elongated shape makes it easier to snap off both the guard and inoculation needle if the syringe barrel is inadvertently held for some reason and someone hits the syringe.
Several other devices have inoculation needles moving through a protective guard which is smaller than the syringe barrel near the insertion tip of an inoculation needle. For instance see U.S. Pat. No. 2,925,083 to Craig, U.S. Pat. No. 4,911,693 to Paris, or U.S. Pat. No. 5,135,510 to Maszkiewicz et al. The insertion point can be seen easier with the latter mentioned devices since the guard is of much smaller diameter, but the inoculation needle still remains at the end of an elongated device. It is much easier to snap an elongated device when it gets inadvertently held near one end. The leverage is such that there are times when an inoculation needle could be exposed just because the syringe barrel got caught in some unusual manner.
None of the above inventions have recognized the fact that an inoculation needle can be drawn back into the syringe barrel to compact the unit that is thrown away. Other inventions illustrate devices which use a spring to retract an inoculation needle inside a plunger. For instance see U.S. Pat. No. 4,994,034 to Botich et al., U.S. Pat. No. 5,017,187 to Sullivan, or U.S. Pat. No. 5,019,044 to Tsao. These devices, however, can not accept conventional inoculation needles as the needles used in these devices are either spring loaded during assembly, or are specially configured for the device to function properly. In addition, all off these devices have a plunger entering from the rear of a syringe barrel in a manner similar to that used in a conventional syringe. This means there has to be some type of sliding surface between the syringe barrel and the plunger which is open to the atmosphere. This sliding surface is a possible source of contamination.
Thus there appears to be a need for a syringe which can hold inoculation fluid in a volume which does not have sealing surfaces exposed to the atmosphere. This would reduce the possibility of possible contamination as the plunger is pulled out and pushed in. In addition a need exists to have a syringe which uses conventional needles which can be retracted into both the plunger and, the syringe barrel. This would simplify the devices used use in current medical facilities. A need also exists to have a double surface surrounding a used needle to provide additional protection against exposure as compared with those instances where only a single surface of a syringe barrel is used. And lastly, a device should be compacted in its disposal state so as to reduce the possibility of inadvertent breakage of an elongated object when the device is caught in some unusual manner.